Re: [xml-dev] ANN: a portable data component -- length

["Pete Cordell" <petexmldev@codalogic.com>]

Original Message From: "Liam R E Quin" <liam@w3.org>
To: "Costello, Roger L." <costello@mitre.org>
Cc: <xml-dev@lists.xml.org>
Sent: Saturday, April 09, 2011 5:00 PM
Subject: Re: [xml-dev] ANN: a portable data component -- length


>
> On Sat, 2011-04-09 at 11:10 -0400, Costello, Roger L. wrote:
>
>> Here is the altitude of an aircraft, expressed in both feet and meters:
>>
>>      <altitude>
>>          <feet>12000</feet>
>>          <meters>3657.6</meters>
>>      </altitude>
>>
>> It is important that the two length values are consistent:
>
> The right way to mark this up in most cases is to store only one value
> and convert as needed.
>
> See Normal Form in database theory: information should never be
> duplicated. That way it can't get out of sync.
>
> So my answer is simply, "don't do this."
>
> Instead, e.g.
>  <measurement>
>    <name>altitude</name>
>    <value units="m">3657.6</value>
>  </measurement>

I agree with the main thrust of your argument, but to me your final example 
seems little better than:

  <object>
    <name>altitude</name>
    <value units="m">3657.6</value>
  </object>

I would say XML already has a notation for specifying what is a name and 
what is a value so there's no need to create an XML syntax that recreates 
that.

I would rather do:

<altitude>3657.6</altitude>

and have it part of the definition that the value of altitude is always in 
meters, and in fact all lengths throughout the entire system are in meters. 
Possibly a bit utopian, but to do otherwise you take the risk of loosing 
space craft while entering the orbit of Mars!

Pete Cordell
Codalogic Ltd
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